A Christian who becomes a Satanist has committed apostasy. So those who apostasize are saved? (Respectfully asking.)
The devil cannot inhabit the temple of God 2 Cor. 6:15-16. 2 Cor. 4:4 tells us the Holy Spirit is greater than the devil.
I am the temple of the living God. And His Spirit lives/dwells within me.
So, no way can your scenario be valid. Besides who in their right mind would want to return to the life He saved us from? Not me ... would you, or have you considered it, Robert?